Inflammation is the response by the body to infection, irritation or injury; wherein the immune cells of the body are activated in response to any of these stimuli. Inflammation plays a key role in many diseases not only of the immune cells such as allergy, asthma, arthritis, dermatitis, multiple sclerosis, systemic lupus but also organ transplant, diabetes, cardiovascular disease, Alzheimer's disease, Parkinson's disease, inflammatory and/or irritable bowel syndrome (Di Sabatino et. al., J. Immunol., 183, 3454-3462, 2009), psoriasis, and cancer. An initial inflammatory response to pathogens or injury is necessary and required to fight infection or heal the wound, but sustained or persistent inflammation can lead to any of the chronic disorders; characterized by the production of inflammatory cytokines as, specified above.
Inflammation is characterized by the production of different cytokines such as IL-2, IL-4, IL-10. IL-13, IL-17, IL-21, IL-23, IL-28, IFN-γ, TNF-α, etc., that have been implicated in playing a role in different diseases. Any drug which can modulate the production of these cytokines would help alleviate the disease symptoms and may also cure it. Ca+2 signals have been shown to be essential for diverse cellular functions in different cell types including differentiation, effector functions, and gene transcription in cells of the immune system as well as regulating the cytokine signaling pathway through calcineurin and nuclear factor of activated T cells (NFAT).
In immune cells, sustained Ca+2 influx has been shown to be necessary for complete and long-lasting activation of calcineurin-NFAT pathways, essential for cytokine production. Engagement of receptors such as T-cell antigen receptor (TCR), the B-cell antigen receptor (BCR), and the Fc receptors (FcR) on mast cells, macrophages, and NK cells, leads to the tyrosine phosphorylation and activation of phospholipase C-γ (PLC-γ). PLC-γhydrolyzes phosphatidylinositol-3,4-biphosphate (PIP2) to the second messengers, inositol-1,4,5-triphosphate (IP3) and diacylglycerol (DAG). IP3 binds to IP3 receptors (IP3R) in the membrane of the endoplasmic reticulum (ER) and induces the release of ER Ca+2 stores into the cytoplasma. The decrease in the Ca+2 concentration in the ER induces store-operated Ca+2 entry (SOCE) through plasma membrane Ca+2 channels. SOCE through highly Ca+2-selective Ca+2 release-activated Ca+2 (hereinafter, CRAC) channels constitutes the major pathway of intracellular Ca+2 entry in T cells, B cells, macrophages, mast cells, and other cell types (Parekh and Putney, Physiol. Rev., 85, 757-810, 2005).
The CRAC channel is comprised of two family proteins, one which functions in sensing Ca+2 levels in the ER—the stromal interacting molecules (STIM)-1 and -2 and the other which is a pore-forming protein—Orai1, 2 and 3. The STIM proteins are single transmembrane proteins localized on the ER membrane with their N-termini oriented toward the lumen and containing an EF-hand Ca+2 binding motif. Depletion of Ca+2 from the ER causes Ca+2 to dissociate from STIM, which causes a conformational change that promotes oligomerization and migration of STIM molecules to closely apposed ER-plasma membrane junctions. At the junctions, the STIM oligomers interact with the Orai proteins. In resting cells, Orai channels are dispersed across the plasma membrane and on depletion of Ca+2 from the stores, they aggregate in the vicinity of the STIM punctae. The eventual increase in intracellular Ca+2 concentration activates the calcineurin-NFAT pathway. NFAT activates transcription of several genes including cytokine genes such as IL-2, etc along with other transcription factors such as AP-1, NFκB and Foxp3 (Fahmer et. al., Immuno. Rev., 231, 99-112, 2009).
The role of CRAC channel in different diseases such as allergy, inflammatory bowel disease, thrombosis and breast cancer has been reported in literature (Parekh, Nat. Rev., 9, 399-410, 2010). It has been reported in the art that STIM1 and Orai1 are essential in in vitro tumor cell migration and in vivo tumor metastasis. Thus the involvement of store operated Ca2+ entry in tumor metastasis renders STIM1 and Orai1 proteins potential targets for cancer therapy (Yang et. al., Cancer Cell, 15, 124-134, 2009). Additional literature available on the involvement of CRAC channel in cancer are Abeele et. al., Cancer Cell, 1, 169-179, 2002, Motiani et al., J. Biol. Chem., 285; 25, 19173-19183, 2010.
Recent literature reports the role of STIM1 and Orai1 in collagen dependent arterial thrombosis in mice in vivo and that deficiency in either protects against collagen dependent arterial thrombus formation as well as brain infarction (Varga-Szabo et. al., J. Exp. Med., 205, 1583-1591, 2008; Braun et. al., Blood, 113, 2056-2063, 2009). The role of STIM1-Orai1 mediated SOCE in thrombus formation makes Orai1 a potential target for treatment of thrombosis and related conditions (Gillo et. al., JBC, 285; 31, 23629-23638, 2010).
As the Orai pore channel proteins have been shown to be essential for transmitting the signal induced by the binding of antigens to the cellular receptors on the immune cells, a potential Orai channel interacting drug would be able to modulate the signaling thereby impacting the secretion of the cytokines involved in, as mentioned hereinbefore, inflammatory conditions, cancer, allergic disorders, immune disorders, rheumatoid arthritis, cardiovascular diseases, thrombocytopathies, arterial and/or venous thrombosis and associated or related conditions which can be benefitted by the CRAC channel modulatory properties of the compounds described herein.
Several compounds have been reported in the art as CRAC channel modulators. For example, patent application publications WO2005009539, WO2005009954, WO2006081391, WO2006081389, WO2006034402, WO2006083477, WO2007087441, WO2007087442, WO2007087429, WO2007089904, WO2009017819, WO2009076454, WO2009035818, US20100152241, WO2010039238, WO2010025295, WO2010027875, WO2011034962, WO2012151355, WO2013059666, WO2013059677 disclose the compounds for modulating CRAC channels.